The present exemplary embodiment relates to printing systems. It finds particular application in conjunction with maintaining image quality in print or marking systems with multiple electrophotographic or xerographic print engines. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
Typically, in image rendering or printing systems, it is desirable that a rendered, or printed, image closely match, or have similar aspects or characteristics to a desired target or input image. However, many factors, such as temperature, humidity, ink or toner age, and/or component wear, tend to move the output of a printing system away from the ideal or target output. For example, in xerographic marking engines, system component tolerances and drifts, as well as environmental disturbances, may tend to move an engine response away from an ideal, desired or target engine response and toward an engine response that yields images that are lighter or darker than desired.
Some document processing systems include a plurality of integrated marking engines. In some systems, each integrated marking engine (IME) includes sensors and control loops for maintaining or directing one or more integrated marking engines processes at or toward some ideal or target. For instance, some electro-photographic systems include a hierarchical control scheme. An exemplary electro-photographic system includes level one control loops for maintaining electro-photographic actuators at set points, level two control loops for selecting set points for the level one control loops and level three controls for compensating for residual differences between actual and target values of aspects of the electro-photographic process.
Such controls can provide excellent quality and consistency within the production of an individual engine source. However, differences in sensors, toners or colorants, temperatures, humidities and other parameters and aspects of engine sources can lead to variations between what is produced by a first engine source and what is produced by a second engine source. Variations between the outputs of two or more engine sources can be completely acceptable where entire production runs are produced by a single engine source. However, when component parts of a single product are produced by different engine sources, print to print variations can be problematic.
For example, where a document processor includes two or more integrated marking engines, marking engine to marking engine variations can be perceived as consistency or quality issues. For instance, where facing pages in a booklet are rendered by different print engines, slight variations in registration, gray scale or color between the facing pages can be perceived as a defect, even though when considered separately, the pages would be considered to be of high quality.
One solution to improve engine-to-engine print quality or consistency is to implement evermore sophisticated sensors and control algorithms within individual marking engines. However, such solutions are expensive in both research and development costs and hardware implementations delivered to customers.
There is a need for methods and apparatuses that overcome the aforementioned problems and others.